This invention relates generally to ultrasound imaging, and more particularly, to measuring flow within ultrasound data.
Conventional ultrasound systems are often used to evaluate blood flow, tissue motion and/or strain rate using standard Doppler techniques to measure blood or tissue velocities. These techniques, however, are limited because only the Doppler velocity component oriented along the line of sight can be measured. In many two dimensional imaging cases, such as colorflow and tissue velocity imaging, the line of sight limitation is ignored, primarily due to different positions in the two dimensional space having different Doppler angles. Thus in these cases, only relative velocity rates and direction of motion are generally used and more quantitative information is obtained using pulsed Doppler. In pulsed Doppler, a sample volume may define a unique point in space and the user may specify a flow direction or angle to compensate for the Doppler angle effect. Even then, flow velocity components in the elevational plane, or normal to the imaging (azimuthal) plane, are ignored.
A process called triangulation has been used to eliminate the fundamental line of sight limitation. A sample volume is interrogated in the imaging plane using two different angles, thus providing a mechanism for calculating the two dimensional velocity components to better quantify the flow velocity. The data may be acquired by sequentially transmitting and receiving using two separate steering angles, thus decreasing the overall frame rate, or by separating the transducer elements of the ultrasound probe into separate apertures that transmit and receive at two separate angles simultaneously. While this method accounts for flow velocities measured in the imaging plane, there is no accounting for the third velocity component in the elevational plane.
Therefore, analysis of flow within a volume is limited because flow velocity components that are outside the current imaging plane are not determined.